Embodiments of the present invention generally relate to an apparatus and method for expanding a tubular in a wellbore. More particularly, apparatus and method relate to a top anchor for a bottom hole assembly having an expandable tubular, an expansion member, the top anchor being configured to affix the expandable tubular to a downhole tubular.
In the drilling of oil and gas wells, a wellbore is typically formed using a drill bit disposed at a downhole end of a drill string that is urged downwardly into the earth. After drilling to a predetermined depth or when circumstances dictate, the drill string and bit are removed and the wellbore is lined with a string of casing. An annular area is thereby formed between the string of casing and the formation. A cementing operation is then conducted in order to fill the annular area with cement. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas or zones behind the casing. The drilling operation is typically performed in stages and a number of casing or liner strings may be run into the wellbore until the wellbore is at the desired depth and location.
Two challenges facing the Oil & Gas industry are accessing new reservoirs that currently cannot be reached economically and maintaining profitable production from producing older fields. Expandable tubular technology was initiated by the industry need to reduce drilling costs, increase production of tubing constrained wells and to enable operators to access reservoirs that could otherwise not be reached economically. Expanded casing applications concentrate on reducing the telescopic profile of well designs through a downhole tube expansion process.
Wellbores are generally provided with one or more casings or liners to provide stability to the wellbore wall, and/or to provide zonal isolation between different earth formation layers. The terms “casing” and “liner” refer to tubular elements for supporting and stabilising the wellbore wall. Typically, a casing extends from surface into the wellbore and a liner extends from a certain depth further into the wellbore. However, in the present context, the terms “casing” and “liner” are used interchangeably and without such intended distinction.
In conventional wellbore construction, several casings are set at different depth intervals, and in a nested arrangement. Herein, each subsequent casing is lowered through the previous casing and therefore has a smaller diameter than the previous casing. As a result, the cross-sectional area of the wellbore that is available for oil and gas production decreases with depth.
To reduce the loss of diameter each time a new casing string or liner is set, a cold working process has been developed whereby the casing or liner can be expanded by up to 25% in diameter after being run down-hole. The applications can be grouped into two main categories, being Cased hole and Open hole. Cased hole work is mainly done during the work over or completion phase of a well. The open hole expandable liner products are used during the drilling period of a well. Open hole applications is where expandable technology brings real advantages to the operator. The technology enables for instance slimmer well profiles, an increased inner diameter at target depth or the drilling of side tracks of existing wellbores.
Herein, one or more tubular elements are radially expanded at a desired depth in the wellbore, for example to form an expanded casing, expanded liner, or a clad against an existing casing or liner. Also, it has been proposed to radially expand each subsequent casing to substantially the same diameter as the previous casing to form a monodiameter wellbore. The available inner diameter of the wellbore remains substantially constant along (a section of) its depth as opposed to the conventional nested arrangement.
U.S. Pat. No. 6,325,148 discloses an apparatus for performing a downhole operation from the surface of a well. The apparatus comprises a tubular body forming a wall and a ring member disposed around the body. The ring member includes a plurality of slips and is held in frictional contact with an inner surface of an outer casing by a spring. A locking member mounted to the wall of the tool selectively prevents motion of said ring until said locking member is unlocked responsive to expansion of the wall of the tubular body.
U.S. Pat. No. 7,992,644 discloses a method of repairing a damaged portion of a casing in a wellbore. The method includes running a bottom hole assembly (BHA) into the wellbore on a conveyance and locating the BHA proximate the damaged portion. The method further includes engaging an inner wall of the casing with a friction member, rotating the conveyance thereby rotating a portion of the BHA, and maintaining a portion of the BHA stationary with the friction member. The method further includes pulling the inner string, thereby engaging the inner wall of the casing with an anchor of the BHA and disconnecting a frangible connection with the anchor. An inner string is coupled to an expansion member and pulling the inner string and thereby the expansion member through an expandable tubular expands the expandable tubular into engagement with the inner wall of the casing thereby repairing the damaged portion.
Although the tools of U.S. Pat. No. 7,992,644 functions properly, the tool has limitations. For instance, the friction member will always engage the casing, also during introduction of the BHA in the casing. The friction blocks of the friction member are required for activation of a top anchor, to prevent the top anchor from moving in axial direction during activation. Due to the friction of the friction blocks however, it is impossible to rotate the BHA while running the tool into the wellbore. Being unable to rotate the BHA limits the length along which the BHA and the expandable liner can be inserted in the wellbore. Also, the BHA is unsuitable for uncased wellbores. As some wellbores tend to be unstable and may collapse onto the expandable liner, rotation may be required to further advance the liner into the wellbore. If the BHA cannot be rotated, the expandable liner may become stuck in the wellbore due to friction, which may ultimately force an operator to plug and abandon the wellbore. In addition, the friction blocks may hinder or disable the return flow of drilling fluid. Also, scaling down the tool is limited due to material limitations of a release ring, i.e. due to the minimum force required to disconnect the frangible connection.